Polymeric tetrafluoroethylene dispersions



. PoLyMERIoTTETRAFLUOROE HYLE E a DISPERSIONS H I Seymour GeorgeBankofi, Terre Haute, Ind.,"as

sig-nor to KL du Pont de Nemours & Company, V WilmingtomuDeL', acorporation-f Delaware:

DrawingQ 'fAbpucauoh Ju1 27, 1949,'

j Serial No. 107,135

5 o1aii 's.

This invention relates to polymeric tetrafluor'oethylene dispersionsand; more particularly,- to

an improved proce forpreparing'aqueous colloidal'disper'sions ofpolytetrafluoroethylene."

aqueous colloidal-dispersion has been obtained by carrying out thepolymerization'of tetrafiuoro ethylene in aqueous medium in the presenceof particular organic peroxide cataIyStS-fsuch asdisuccinie acidperoxide as disclosed momma States application Serial No. 713,3 85:filedNovem-' ber' 30, 1946 in thename of MalcolmMi Renfrew;

now United States Patent 2534;058. A serious disadvantage of thisprocedureisthat the c'olloid is unstable and is coagulateda-t'very lowpolymer concentrations by the agitation' necessary to dis-' v solve thegaseous tetrafluoroethylene monomer in the aqueous medium. The result isthat the de sired'colloidal polymer isobta'in'e'd in a'state of:

high dilution with the aqueous reaction medium,

necessitating the handling of large amounts-oi waterfor a given amountof polymer. A method for overcoming this difficulty is described-infUnited States application Seria1-No.-'2;3,4(l0, filed April 26,1948,'infthe name of'Kenneth L.-Be'rry,'

refiled as Serial No. 225,677 on May 10;1951,

involving the use, as a stabilizer; during polymerization, ofcompletelyhalogenated poly'fluoro ethylenes, (i. e., fluid, saturated"halocarbons' which are highly inert an'd -doi notinterfere chemically inthe polymerizationx Ho ever; flthe*-- liquid halocarbons which are'suitable -forthis.

' purpose are not-as readiiy'availableor aside-f sirable'for commercialuse and are-,"therefore expensive.

An object of the present inventior ris w-prqvide an improved process forpreparing aqueous colloidal' dispersions of 'p'olytetrafluoro'ethylen Afur-ther object is to provides'ucha probe which i jmorel economical andsatisfactory than 'thoseheretofore known. 'Other"objects- -wi1l be"apparent fromthe"description of theinvention v given hereinafter. i

(The above vobjects are accomplished according to the present" inventionby the step of carryingoutthe polymerization or-the monomeric tetr'a-'fiuoroethylene dissolved in 1 an aqueous medium in the presenceof awater-soluble polymerization catalyst and in the presence .;of p0;L%-'12byweight of the aqueousmediumjiof a saturated hydrocarbon having morethan 12 carbo'nxatomsi and. which is'liquid under the polymerizationconditions; Ithas been. found that these par-'-.- ticular hydrocarbonsact as stabilizers and-per mit asurprisin increase in the concentrationofm in the aqueous I J hydrocarbon andfa'water solub1e"catalysticolloidal polytetrafluoroethyl'ene in "the aqueous dispersion before"coagulation of the. polymer; takesplacegfl" 1 I] The polymerization ofthe tetrafiuoroethylene" m'edium'containing the'jspec'ified ried out inaccordance Withthe' knowni'gen v procedures. Pressuresflof from 1 to1000 atmos 'pheres and temperatures of 0 C. to C. are

normally; used, as disclosed -;-in United States v Patent2,39.3;967.;rAlthough optional,=. it' is usually advantageous itorainclude with the.polymerization a.

catalyst alpolymeri-zation promoterasuch v as;

sodium 'bisulfite, especially when the polymerization isgrcarriedfloutat :the slower temperatures-in thisran 2i..;:.e.;afrom; 0C. to. 50 C.*In-addi-u tion, a small; amount; of. water-solublezferrous:

salt, e. g; ferrous sulfate, is advantageously. present inamountgsufficient to provide from0'.2:t0 -59 Darts2 per;mil1ion"of-ferrous ions vbased .on the weight ofgth ye aqueous medium,,i.je'.-, the water; v

I'n a preferred procedure for carrying outzthe present inventiom areaction mixture comprisg;-- distilled-: .or,demineralizedz-iwaterlto*which a has 'been' added small amounta;0f;ammonium jpersulfatejor other water-solublelperoxy polymerization'catalyst, sodium'bisulfite, a trace oi g y a, ferrous iron: salt, and.-1%'-5'%', based on the I we ht; .of the. aqueous medium;.-, i'.:-e.,-thewater; of .,a 's-saturated1hydrocarbon' of more than 12 carbon atomswhichis liquid under -thereaction x conditionsiiis.charged intov apres-sure vessel and the '-v essel3;,is;; evacuated.Tetrafluoroethyleney v monomeris introduced untily'asuitable pressureye. g., about6Q;.lbs.Asq.?in., is attained-" ithe closedi r ssure izessehis;Jtherriheatedlto-iabout 50--- with agitation and withvcontinuousaddition- 0f sufiicient tetrafluoroethylene. ltoimaintain' the; ide

sired pressure .untilithe colloidal polymer formed begins to coagulate.Ther results aucolloidal dispersion of high. molecularweig'ht,filmz-vforming gpoly neric tetrafluoroethylenelcontaining up to l 5 of colloidalpolymer; 2

/,. 1h ;1inventiont :is illustrated in 'zfurtherdetail bygthefollowingexamplesinwhich the proper tions of, the reactants are expressed mpartsby 1 v weight unlessotherwise specified. .1; v .t Eitdrr'tpll Twohundred parts of distilled *wata 0,1 part. of ammonium 'persulfate,=-0'.05*-part of sddi I bisu1fite';- '0. 002 part of ferrous sulfate hetfa hydrate and 2 .3 parts'of tetradecane are mined inatpressure'vesse1-(ha ving a volume-"capacity of- 325 parts ofwater at-roointemperature) and i the mixture is maintained at 25 C. The vessel'isevacuated to remove air and then pressured;

to 51 lbs/sq. in. with tetrafiuoroethylene gas.

tetrafluoroethylene. At the end of this time there is obtained anaqueous dispersion of high molecular weight, film-formingpolytetrafluoro ethylene of 4.3 solids content. A control experiment isconducted in aniden- 1 tical manner'with the sole exception that the'tetradecane is omitted.

polymer begins after twelve minutes and the above-defined carbon chainlength in stabilizing colloidal dispersions of high molecular weightCoagulation of the agitation is then discontinued. There is obtained anaqueous polytetrafluoroethylene dispersion containing only 0.7% solids.

Example II The process of Example I is repeated under thev sameconditions and withthe same proportionsofreactants'With the singleexceptionthat parafiln waxes havin melting points below 100* C. Sincethe hydrocarbon must be liquid at the temperature of polymerization,obviously paraffin wax must be selected with due regard to its meltingpoint so that it may meet this requirement. It is immaterial how manycarbon atoms the hy drocarbon contains above 12 so'long as'it is liquidat the polymerization temperature. These hy drocarbons are added to theaqueous medium in proportions of from 0.1%-12% by Weight based on thetotal weight of the aqueous'medium. It

"is preferred to use a proportion of from 1%-5% of the hydrocarbon asbest results are obtained I Within that range.

The efiectiveness: of the hydrocarbons of the polytetrafluoroethylene isquite surprising. Fur- I 3.9 parts of cetane is substituted for the 2.3parts of t'etradecane of Example I. After 2J2 h'ours at fjQC. and undera tetrafluoroethylen pressure of 15 0 lbs/sqin., there, isv obtainedacolloidal dispersion of polytetrafluoroethylene contai 84% solids.

nine.

. Example III Y v V. A pressure reactor having a volume capacity-of 159:parts :of water at room temperature, and- .fitted' with an agitatorcapable ofbeing rotated at'40 R. P. M., is charged with 113.6 parts ofde- ;minera1ized water, 0.076Ipart of disuccinic acid peroxideand 0.5part-of parafiin wax meltingat- 54?. C.-58. C. The vessel is evacuatedto remove air; pressured to 300-350 lbs/sq. inwith tetra-p fiuoroethylene and heated to 65 CfWifih continuous agitation. After aninduction periodof 5- minutes and a reaction-time of 5 5 minutes there Iis obtained'a 513%. solids: dispersion of hi'gh -molecular .weight,film-forming polytetrafiuoroethylene.; The dispersion contains6.56'pa'rts of poly-' tetrafluoroethylene which correspondsfto'a-95.3%

conversion of the monomer to colloidal polymer.

Example. 1V

matelyi320', parts :of a high boiling mineral oil .Lcomprising.a-mixture. of hydrocarbons havingjan average of 25-30 carbon atoms ischarged intoa .reasttion vessel fitted. :with a mechanical agitater.Thereaction. vessel is closed, heated to" B5"; ,C pressured. withtetrafluoroethyleneat 3.0.0451 1bs./sq...in., andthetagitatorrotated-ata speed .off38': R.v P. After tWo hOurs-and M Aminutes thereiis :obtaineda dispersion of"'poly-' 9' without dangergofcoagulation of. the .polyrneriat tetrafluoroethylene containing 4.6%colloidal solid polymer.

It will be understood that the above examples are merely'illustrativeandthat the invention broadly comprises polymerizing tetrafiuoroethyl eneinan aqueous medium in'the presence offa water-soluble polymerizationcatalyst. and in the presence of 0.1%-12%, by weight of the-aqueousmedium, of a saturatedhydrocarbon having more than 12 carbon atoms andwhich is liquid under the polymerization conditions.

thermore, this efiectiveness is dependent on the particular hydrocarbonsand under the particular conditions defined herein. That is, thesehydrocarbons are etffective yvith tetrafiuoroethylene only in aqueous;polymerization systems, ,in the presence of water-solublepolymerizationv catalysts, and @when the hydrocarbon isus ed inproportions of from 0.1% to not appreciably above 12% by weight ofthereaction medium. v s

That the- 12-.carbon limitation of the hydrocar bon is critical, isevident from the results of the followingexperiments. In a series ofexperiments, carried; out similar to; theprocess; of Examamples -I andII. but in which thetetradecane; and cetane of those examples-wasreplaced bydodecane. decane, isooctaneand decahydronaphthalene;respectively, no polymerization took place at all in the presence ofisooctane or decahydronaphthalene,and only very small amounts ofcoagulated, 1 low molecular weight 'tetrafiuoroethylenetelomer waxeswere obtained in the;

12 carbonatoms in the process of this. inventionv isapparently due totheir low solubility in water.

Even though theseghydrocarbons are potentially telogenic; theiriwater-solubility is so low that. thereis insuificient concentration ofthese.hydro-' g a V v carbon existingin theaqueous phase.(which'is AmixturegofBOOO -parts .of distilled water; 3 parts of disuccinic acidperoxide and approxi the site. of the; tetrailuoroethylene polymerizae:tion); to inh'ibittheformation of a high molecular-1:

weigha ou tetrafluoroethylene, polymen, On.

theoither-hand, the small amount of hydrocar-s bonipresent as aphaseseparate from-the aque .-i.=' ous -solution is sufIi ientJtostabilize the colloidal;

dispersion of polytetrafluoroethylene againstco-z .1 d r agulationcaused by the agitation necessary dur: i ing polymerization. i l n Thesehydrocarbons are emcient stabilizing: agen si against coagulationandpermit thorough agitatipn of the contents of thereaction. vessel"- lowconcentrations. iBy the; use ofzagitatiomthe 1 polymerization cyclejmaybe appreciably reduced: in time. Also, at the end of the.cycle,these.-thy=-;

formedp'i .while -leavin'g. the. colloidal r polymera'inithe aqueousmedium.

drocarbons rise'to the'surface..of th'eweaction mixture, and thus.facilitatertheir removal.

temperatures is tha-tinseparating and .lising 'tdthe jsurraceofgt hereaction mixture, they entrain and removeany coagulated'polymer thatmaybe particlesiz cf f 'I'he-spresent inventionitis primarily concernedwithgthe. ..polymerization. of .tetrafluoroethylene.

However. it-isnotrestricted' to' the iormation oi homopiolymersr of;tetrafiuoro'ethylene "as it 'is en- L tirely operative, and maybe iusedadvantageously in, the, formation of copolymers oftetrafluorofluoroohloroethylene, vinyl. .fluoride and. vinyle .idine,Ifluoride, vinyl acetate-,1-;acrylonitrile;* and similar .olfganiccompounds ,copolymerizableawith :tetrafluorqethylene, and, containinga=terminal carbonate-carbon double bond The polymerization is carriedout in the presence of a polymerization catalyst, such catalysts and thefavorable proportions in which they are used, being known in the priorart. As the polymerization takes place in an aqueous medium, thecatalyst must be water-soluble. It may be either an organic or inorganiccompoundas illustrated in-the examples, the peroxy compounds beingpreferred. Numerous polymerization catalysts are disclosed in U. S.Patents 2,393,967 and 2,394,243 as well as in the aforementioned Renefrew application Serial No. 713,385. These catalysts are normally usedin the proportion of 0.001% to 5%, based on the weight oftetrafluoroethylene employed, with a proportion of 0.01% t0'2%preferred, although smaller or larger' amounts may be used. Disuccinicacid peroxide is the preferred specific polymerization catalyst.Preferably, the air is removed from the reaction vessel before the startof the polymerization.

The dispersions of this invention are useful for fabricating thepolymers into a variety of forms. Films can be cast by baking flow-outs,and in a similar manner coatings of the polymers can be applied tometal, fabrics, wood, ceramics and carbon. Coatings on metal in the formof wire, foils, materials-handling equipment such as chemical reactorsand pipe lines, structural forms, and porous articles made by casting orpowder metallurgy techniques, are of particular value for theirinertness to moisture, corrosive chemicals, solvents and electrical andmechanical stresses. Impregnations are possible because of the smallparticle size of the polymers. Fabrics are advantageously impregnated toconfer water repellency by the procedure disclosed in copendingapplication Ser. No. 726,717, filed February 5, 1947 in the name of K.L. Berry now U. S. Patent 2,532,691, and glass fabrics impregnated andcoated with the dispersions have unique stability and other desirableproperties such as flexibility, high dielectric strength andimpermeability. Coated glass fabrics prepared in this way can be used asfuel pump diaphragms and in the fashioning of resistor cores.Polytetrafiuoroethylenecoated glass fabrics can also be laminated byheat and pressure to give stiffer products. Casting molds formed fromthe coated glass fabric by heat and pressure can be used as molds forlowmelting metals. Coatings on carbon and ceramics confer moistureprotection with resultant increase in surface resistivity and resistanceto tracking by an electric arc. The dispersions are also useful asadhesives, particularly for polytetraiiuoroethylene sheeting, mica,metals and ceramics. In particular, a polytetrafiuoroethylene surfacecan be permanently joined to a solid substance by application of adispersion of the type provided by this invention containing at least ofthe polymer, drying the joint by heating at not more than 100 C. andsubsequently heating the structure to above 327 C.

The hydrocarbon stabilizersof this invention may be used to advantage incombination with certain dispersingaragents .to-give-stable aqueousdispersions. iof. .acolloidal v-tetr'afluoroethylene=i ofgreatlyiincreased concntrations, e. -:g.,.up; to 60 concentration;ancbzrhigheru -The combination: of

these: hydrocarbon; stabilizersiwith. salts. of poly: fiuorocarboxylic,acidshas-u dispersing agents Tis fullyclisclosed andaclaimedin U. S.application Serial No.11 01133,,filedgofleven date herewith in the nameof K. L. Berry and-.refiled on June 29;.1-9501as-Seria1;No::171,241:Serial No. 171,241 was, in turn, refiled March 6, 1951 as Serial No.214,233, this latter application having now issued as U. S. Patent2,559,772. From 0.01% to 10%, by weight of the aqueous medium, of a saltof a polyfluorocarboxylic acid is added to the aqueous medium. Thepreferred polyfluorocarboxyl ate dispersing agents are the ammonium andalkali metal salts of. acids having the formula H(CF2)nCOOI-I wherein nis an even numberfrom 6 to 10. These salts may be prepared according tothe method described in U. S. applica-- tion Serial No.-65,065, filedDecember 13, 1948, by K. L. Berry, now issued as U. S. Patent2,559,629..

This method consists in oxidizing, with a per-- manganate as theoxidizing agent, a po1yfluorov alkanol of the formula I-I(CE2) nCHzO'H,wherein. Y a is an even number from 6 to 10. These polyfiuoroalkanolsare themselves obtained by heating at a temperature between 75 C. and350 C.,.

inthe presence of a free radical-producing catalyst, a mixture ofmethanol with tetrafluoroethylene, in accordance with the proceduredescribed in U. S. application Serial No. 65,063, filed December 13,1948, by R. M. Joyce, now-issued as U. S. Patent 2,559,628. v

In these tetrafluoroethylene polymerization systems involving the use ofpolyfiuorocarboxylate dispersing agents, the paraffin waxes are thepreferred hydrocarbon stabilizing agent and the polymerization ispreferably carried out at about 70 C. in the absence of any activatorssuch as bisulfite and ferrous ions. In this system the hydrocarbonfunctions to delay and minimize precoagulation during thepolymerization. Even if a parafiin wax is not used, it is preferred touse a higher molecular weight hydrocarbon, i. e., hydrocarbons of morethan 16 carbon atoms. These higher molecular weight hydrocarbons givebetter results apparently because the fluorocarboxylate exerts somesolubilizing effect on the hydrocarbon stabilizers of lower molecularweight.

As many apparently widely different embodiments of this invention may bemade without de parting from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

The invention claimed is:

1. In a polymerization of monomeric tetrafiuoroethylene dissolved in anaqueous medium to obtain a colloidal dispersion of polymerictetrafluoroethylene, the step of carrying out said polymerization at atemperature of 0 C. to C. in the presence of a water-soluble peroxypolymerization catalyst .and in the presence of 0.1%-12%, by weightof'sai-d aqueous medium, of a saturated hydrocarbon'having more than 12carbon atoms and which is liquid under the polymerization conditions.

2. Process as set forth in claim 1 wherein said saturated hydrocarbon isa parafiin wax having a melting point below the temperature at whichsaid polymerization is carried out.

3. Process as set forth in claim 1 wherein said

1. IN A POLYMERIZATION OF MONOMERIC TETRAFLUOROETHYLENE DISSOLVED IN ANAQUEOUS MEDIUM TO OBTAIN A COLLOIDAL DISPERSION OF POLYMERICTETRAFLUOROETHYLENE, THE STEP OF CARRYING OUT SAID POLYMERIZATION AT ATEMPERATURE OF 0*C. TO 100* C. IN THE PRESENCE OF A WATER-SOLUBLE PEROXYPOLYMERIZATION CATALYST AND IN THE PRESENCE OF 0.1%-12%, BY WEIGHT OFSAID AQUEOUS MEDIUM, OF A SATURATED HYDROCARBON HAVING MORE THAN 12CARBON ATOMS AND WHICH IS LIQUID UNDER THE POLYMERIZATION CONDITIONS.